vo_opengl: add mechanism to retrieve Display from EGL context

The VAAPI EGL interop code will need access to the X11 Display. While
GLX could return it from the current GLX context, EGL has no such
mechanism. (At least no standard one supported by all implementations.)
So mpv makes up such a mechanism.

For internal purposes, this is very rather awkward solution, but it's
needed for libmpv anyway.

3 files changed, 33 insertions, 1 deletions

diff --git a/libmpv/opengl_cb.h b/libmpv/opengl_cb.h
index bd694b61d4..112f254a59 100644
--- a/libmpv/opengl_cb.h
+++ b/libmpv/opengl_cb.h
@@ -126,6 +126,16 @@ extern "C" {
  * up until mpv_opengl_cb_uninit_gl() is called. If the name is not anything
  * you know/expected, return NULL from the function.
  *
+ * Windowing system interop on Linux
+ * ---------------------------------
+ *
+ * The new VAAPI OpenGL interop requires an EGL context. EGL provides no way
+ * to query the X11 Display associated to a specific EGL context, so this API
+ * is used to pass it through.
+ *
+ * glMPGetNativeDisplay("x11") should return a X11 "Display*", which then will
+ * be used to create the hardware decoder state. (On GLX, this is not needed.)
+ *
  * Windowing system interop on MS win32
  * ------------------------------------
  *
diff --git a/video/out/opengl/x11egl.c b/video/out/opengl/x11egl.c
index 53cd5ae677..87e0e89fff 100644
--- a/video/out/opengl/x11egl.c
+++ b/video/out/opengl/x11egl.c
@@ -20,6 +20,8 @@
  * version 2.1 of the License, or (at your option) any later version.
  */
 
+#include <assert.h>
+
 #include <X11/Xlib.h>
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
@@ -29,11 +31,21 @@
 #include "common.h"
 
 struct priv {
+    Display *x_display;
     EGLDisplay egl_display;
     EGLContext egl_context;
     EGLSurface egl_surface;
 };
 
+static _Thread_local struct priv *current_context;
+
+static void * GLAPIENTRY get_native_display(const char *name)
+{
+    if (current_context && strcmp(name, "x11") == 0)
+        return current_context->x_display;
+    return NULL;
+}
+
 static EGLConfig select_fb_config_egl(struct MPGLContext *ctx, bool es)
 {
     struct priv *p = ctx->priv;
@@ -99,6 +111,8 @@ static bool config_window_x11_egl(struct MPGLContext *ctx, int flags)
     struct vo *vo = ctx->vo;
     bool es = flags & VOFLAG_GLES;
 
+    p->x_display = vo->x11->display;
+
     if (!eglBindAPI(es ? EGL_OPENGL_ES_API : EGL_OPENGL_API)) {
         MP_FATAL(vo, "Could not bind API (%s).\n", es ? "GLES" : "GL");
         return false;
@@ -138,7 +152,10 @@ static bool config_window_x11_egl(struct MPGLContext *ctx, int flags)
 
     void *(*gpa)(const GLubyte*) = (void *(*)(const GLubyte*))eglGetProcAddress;
     mpgl_load_functions(ctx->gl, gpa, egl_exts, vo->log);
+    ctx->gl->MPGetNativeDisplay = get_native_display;
 
+    assert(!current_context);
+    current_context = p;
     return true;
 }
 
@@ -171,6 +188,7 @@ static void mpegl_uninit(MPGLContext *ctx)
         eglDestroyContext(p->egl_display, p->egl_context);
     }
     p->egl_context = EGL_NO_CONTEXT;
+    current_context = NULL;
     vo_x11_uninit(ctx->vo);
 }
 
diff --git a/wscript b/wscript
index f23cf43500..22cc4693d1 100644
--- a/wscript
+++ b/wscript
@@ -173,6 +173,10 @@ main_dependencies = [
         'func': check_true,
         'deps_any': ['stdatomic', 'atomic-builtins', 'sync-builtins'],
     }, {
+        'name': 'c11-tls',
+        'desc': 'C11 TLS support',
+        'func': check_statement('stddef.h', 'static _Thread_local int x = 0'),
+    }, {
         'name': 'librt',
         'desc': 'linking with -lrt',
         'deps': [ 'pthreads' ],
@@ -605,7 +609,7 @@ video_output_features = [
     } , {
         'name': '--egl-x11',
         'desc': 'OpenGL X11 EGL Backend',
-        'deps': [ 'x11' ],
+        'deps': [ 'x11', 'c11-tls' ],
         'groups': [ 'gl' ],
         'func': check_pkg_config('egl', 'gl'),
     } , {